A new wave of aggressive yoga classes incorporates cardio, CrossFit, and even boxing to get fitness results.

There are actual punching bags at Box + Flow, which opened last November in downtown New York. The 50-minute barefoot classes begin with shadowboxing warmups, then shift to sessions on the bags with a high-energy Top 40 soundtrack, then a final session of yoga postures that ends with breathing exercises and a savasana. “It’s yin and yang, fire and water,” said founder Olivia Young, who trained for 10 years at Church Street Boxing Gym and practiced yoga for 15 before starting her own studio. “Yoga allowed me to open up and slow down. But I tend to be very high-energy, and I needed something with more adrenaline.” She cautions, however: “If you're looking to become the best boxer or the best yogi, this is not the right class.”